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1.15.2: Heat Capacities: Solutions: Solutes: Interaction Parameters

  • Page ID
    393964
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    We describe an excess enthalpy \(\mathrm{H}^{\mathrm{E}}\) for a solution prepared using \(1 \mathrm{~kg}\) of water and \(\mathrm{m}_{j}\) moles of solute \(j\) (at fixed \(\mathrm{T}\) and \(\mathrm{p}\)) ion terms of solute-solute enthalpic interaction parameters.

    \[\mathrm{H}^{\mathrm{E}}\left(\mathrm{aq} ; \mathrm{w}_{1}=1 \mathrm{~kg}\right)=\mathrm{h}_{\mathrm{ij}} \,\left(\mathrm{m}_{\mathrm{j}} / \mathrm{m}^{0}\right)^{2}\]

    The corresponding excess isobaric heat capacity is defined by equation (b).

    \[C_{p}^{E}\left(a q ; w_{1}=1 k g\right)=c_{p i j} \,\left(m_{j} / m^{0}\right)^{2}\]

    where

    \[\mathrm{c}_{\mathrm{pij}}=\left(\frac{\partial \mathrm{h}_{\mathrm{ij}}}{\partial \mathrm{T}}\right)_{\mathrm{p}}\]

    Here \(\mathrm{c}_{\mathrm{pjj}}\) is a pairwise solute-solute interaction isobaric heat capacity [1]. From

    \[\mathrm{H}_{1}(\mathrm{aq})=\mathrm{H}_{1}^{*}(\ell)-\mathrm{M}_{1} \, \mathrm{h}_{\mathrm{ij}} \,\left(\mathrm{m}_{\mathrm{j}} / \mathrm{m}^{0}\right)^{2}\]

    then,

    \[\mathrm{C}_{\mathrm{p} 1}(\mathrm{aq})=\mathrm{C}_{\mathrm{pl}^{2}}^{*}(\ell)-\mathrm{M}_{\mathrm{l}} \, \mathrm{c}_{\mathrm{pjj}} \,\left(\mathrm{m}_{\mathrm{j}} / \mathrm{m}^{0}\right)^{2}\]

    From

    \[\mathrm{H}_{\mathrm{j}}(\mathrm{aq})=\mathrm{H}_{\mathrm{j}^{\prime}}^{\infty}(\mathrm{aq})+2 \, \mathrm{h}_{\mathrm{jj}} \,\left(\mathrm{m}^{0}\right)^{-2} \, \mathrm{m}_{\mathrm{j}}\]

    then,

    \[\mathrm{C}_{\mathrm{pj}}(\mathrm{aq})=\mathrm{C}_{\mathrm{pj}}^{\infty}(\mathrm{aq})+2 \, \mathrm{c}_{\mathrm{pjj}} \,\left(\mathrm{m}^{0}\right)^{-2} \, \mathrm{m}_{\mathrm{j}}\]

    Footnote

    [1] For a solution prepared using \(1 \mathrm{~kg}\) of water and \(\mathrm{m}_{j}\) moles of solute (at fixed \(\mathrm{T}\) and \(\mathrm{p}\))

    \[\mathrm{C}_{\mathrm{p}}\left(\mathrm{aq} ; \mathrm{w}_{1}=1 \mathrm{~kg}\right)=\left(1 / \mathrm{M}_{1}\right) \, \mathrm{C}_{\mathrm{p} 1}(\mathrm{aq})+\mathrm{m}_{\mathrm{j}} \, \mathrm{C}_{\mathrm{pj}}(\mathrm{aq})\]

    Hence

    \[\begin{gathered}
    \mathrm{C}_{\mathrm{p}}\left(\mathrm{aq} ; \mathrm{w}_{1}=1 \mathrm{~kg}\right)=\left(1 / \mathrm{M}_{1}\right) \,\left[\mathrm{C}_{\mathrm{pl}}^{*}(\ell)-\mathrm{M}_{1} \, \mathrm{c}_{\mathrm{pjj}} \,\left(\mathrm{m}_{\mathrm{j}} / \mathrm{m}^{0}\right)^{2}\right] \\
    +\mathrm{m}_{\mathrm{j}} \,\left[\mathrm{C}_{\mathrm{pj}}^{\infty}(\mathrm{aq})+2 \, \mathrm{c}_{\mathrm{pjj}} \,\left(\mathrm{m}^{0}\right)^{-2} \, \mathrm{m}_{\mathrm{j}}\right]
    \end{gathered}\]

    Then,

    \[\mathrm{C}_{\mathrm{p}}\left(\mathrm{aq} ; \mathrm{w}_{1}=1 \mathrm{~kg}\right)=\left(1 / \mathrm{M}_{1}\right) \, \mathrm{C}_{\mathrm{p} 1}^{*}(\ell)+\mathrm{m}_{\mathrm{j}} \, \mathrm{C}_{\mathrm{pj}}^{\infty}(\mathrm{aq})+\mathrm{c}_{\mathrm{pji}} \,\left(\mathrm{m}_{\mathrm{j}} / \mathrm{m}^{0}\right)^{2}\]

    Since,

    \[\begin{gathered}
    \mathrm{C}_{\mathrm{p}}\left(\mathrm{aq} ; \mathrm{id} ; \mathrm{w}_{1}=1 \mathrm{~kg}\right)=\left(1 / \mathrm{M}_{1}\right) \, \mathrm{C}_{\mathrm{pl} 1}^{*}(\mathrm{aq})+\mathrm{m}_{\mathrm{j}} \, \mathrm{C}_{\mathrm{pj}}^{\infty}(\mathrm{aq}) \\
    \mathrm{C}_{\mathrm{p}}^{\mathrm{E}}\left(\mathrm{aq} ; \mathrm{w}_{1}=1 \mathrm{~kg}\right)=\mathrm{c}_{\mathrm{pjj}} \,\left(\mathrm{m}_{\mathrm{j}} / \mathrm{m}^{0}\right)^{2}
    \end{gathered}\]


    This page titled 1.15.2: Heat Capacities: Solutions: Solutes: Interaction Parameters is shared under a Public Domain license and was authored, remixed, and/or curated by Michael J Blandamer & Joao Carlos R Reis.